This invention relates to trigger-actuated applicators for multi-component adhesives or fillers of the resin type or the like. More particularly, the invention relates to internal valving control mechanisms of gun applicators that meter the flow of a multi-component compound onto a workpiece in response to operator demand.
Gun-type applicators are useful where materials are applied to a workpiece intermittently by an operator who must exercise judgement as to amount and placement of material. For example, in manufacturing plywood, an adhesive filler is applied to random defects such as knotholes and cracks in the outer plies of panels which may have a subsequent overlayment.
The materials applied by a gun may comprise fluids having a wide range of physical characteristics such as viscosity, densities, and the like. Often the material applied is a mixture or a reaction product of several components. For example, in the plywood manufacturing process indicated above, a commonly used filler-patching compound is a urethane system, produced by mixing tolylene di-isocyanate with a glycol or other hydroxylic component. The two liquid components require vigorous stirring, with a polymerization reaction taking place in emulsion at very high rates. The typical compounds used for patching and filling are designed to be fast curing on the workpiece, which design requirement results in the compound generally having a very low pot life.
As a consequence of system application requirements such as fast cure time, the major drawback in the use of guns heretofore known has been their general propensity to foul and plug with compound that has set or partially cured. These drawbacks are magnified by intermittent use and low flow rates through the apparatus which are characteristic of the patching and filling use previously described.
The known gun cleaning techniques require solvent flushes and disassembly on a regular basis. Solvent cleaning is generally not enough since the gun interiors are often complex, presenting many surface areas for accumulation of partially cured compound. The solvent flushing technique employed to clean most guns often involves backflow into component supply lines which must be purged with fresh component material when the gun is placed back in use resulting in waste of component material and the creation of a disposal problem.
It is also desirable that a gun be operable without waste or loss of compound through leakage and dripping from the discharge end of the gun. Such dripping is not only an economic loss but creates production difficulties as the compound fouls the workpiece and work station.